Wire heated tube with temperature control system for humidifier for respiratory apparatus

Patent metadata

Field	Value
Publication number	US-9572949-B2
Application number	US-201414169714-A
Country	US
Kind code	B2
Filing date	Jan 31, 2014
Priority date	Feb 1, 2013
Publication date	Feb 21, 2017
Grant date	Feb 21, 2017

Abstract

A PAP system for delivering breathable gas to a patient includes a flow generator to generate a supply of breathable gas to be delivered to the patient; a humidifier including a heating plate to vaporize water and deliver water vapor to humidify the supply of breathable gas; a heated tube configured to heat and deliver the humidified supply of breathable gas to the patient; a power supply configured to supply power to the heating plate and the heated tube; and a controller configured to control the power supply to prevent overheating of the heating plate and the heated tube.

First claim

What is claimed is:

1. A sensing circuit for a heated conduit for use in a respiratory apparatus, the sensing circuit comprising:
a sensing wire coupled to a heating circuit for the heated conduit;
a temperature sensor coupled to the sensing wire and configured to measure the temperature of the heated conduit;
a sensing resistor coupled to the sensing wire and configured to provide an output to indicate the temperature measured by the temperature sensor; and
a bias generator circuit configured to provide a reference voltage to the sensing resistor to allow determination of the output as a function of a voltage drop across the sensing resistor during both heating on and heating off cycles of the heating circuit,
wherein the bias generator includes a track and hold circuit configured to measure a voltage of the sensing wire and provide the measured voltage to the bias generator circuit, wherein the bias generator circuit is configured to adjust the reference voltage as a function of the measured voltage.

2. The sensing circuit of claim 1 , wherein the track and hold circuit comprises a capacitor configured to record the measured voltage and provide the measured voltage to the bias generator circuit.

3. The sensing circuit of claim 1 , wherein the track and hold circuit measures the voltage of the sensing wire during a sampling period prior to providing the measured voltage to the bias generator.

4. The sensing circuit of claim 3 , wherein the sampling period is approximately 2 to 10 milliseconds long.

5. The sensing circuit of claim 3 , wherein the sampling period is approximately 1 to 25% of a duty cycle of the heating circuit.

6. The sensing circuit of claim 5 , wherein the sampling period is approximately 2 to 20% of the duty cycle of the heating circuit.

7. The sensing circuit of claim 5 , wherein the sampling period is approximately 5 to 15% of the duty cycle of the heating circuit.

8. The sensing circuit according to claim 1 , wherein the track and hold circuit is configured to measure the voltage of the sensing wire during a heating on cycle.

9. The sensing circuit according to claim 1 , wherein the track and hold circuit is configured to measure the voltage of the sensing wire during a heating on cycle and during a heating off cycle.

10. The sensing circuit according to claim 1 , wherein the reference voltage of the bias generator circuit includes a bias source voltage.

11. The sensing circuit according to claim 10 , wherein when the heating circuit is on the bias source voltage is added to the measured voltage to provide the reference voltage.

12. The sensing circuit according to claim 10 , wherein when the heating circuit is off the reference voltage is equal to the bias source voltage.

13. A control system for a heated conduit for use in a respiratory apparatus, the control system comprising:
a power supply to provide power to the heated conduit;
a heating control circuit configured to control heating to obtain a predetermined temperature; and
a sensing circuit according to claim 1 .

14. A heated conduit comprising a control system according to claim 13 .

15. A control system for a heated conduit for use in a respiratory apparatus, the control system comprising:
a power supply to provide power to the heated conduit;
a heating control circuit configured to control heating to obtain a predetermined temperature;
a sensing circuit configured to indicate the temperature of a sensor positioned in the heated conduit; and
a bias generator circuit configured to provide a current to the sensor from a current source to allow for a voltage drop through the sensor that is recordable by the sensing circuit so that the temperature of the heated conduit is continuously monitored independent of whether the heating control circuit is on or off.

16. The control system of claim 15 , wherein the current source includes a current mirror circuit.

17. The control system of claim 15 , wherein the bias generator circuit comprises a pair of resistors, the pair of resistors being positioned on an opposite side of the sensing circuit from the current source and being configured to receive voltage from the heating control circuit.

18. The control system of claim 15 , wherein the bias generator circuit is configured so that a voltage provided to the sensing circuit that varies only as a function of the temperature of the sensor and does not vary as a function of an ON/OFF state of the heating control circuit.

19. A control system for a heated conduit for use in a respiratory apparatus, the control system comprising:
a power supply to provide power to the heated conduit;
a heating control circuit configured to control heating to obtain a predetermined temperature;
a sensing circuit including a sensing resistor configured to provide an output to indicate the temperature of a sensor positioned in the heated conduit; and
a bias generator circuit configured to provide a reference voltage to the sensing resistor to allow determination of the temperature of the heated conduit as a function of a voltage drop across the sensing resistor during both heating on and heating off cycles,
wherein a direction of the voltage drop across the sensing resistor changes when the heating circuit is on compared to when the heating circuit is off.

20. The control system according to claim 19 wherein the sensing circuit further includes a full wave rectifier circuit that adjusts the output.

21. The control system of claim 20 , wherein the rectifier is configured to transform the polarity of the output of the sensing circuit so that the polarity of the output of the sensing circuit is the same regardless of whether the heating control circuit is in the ON state or in the OFF state.

22. The control system of claim 21 , wherein the rectifier is configured to transform the polarity of the output of the sensing circuit so that the polarity is uniformly positive irrespective of whether the output of the sensing circuit is positive or negative.

23. The control system of claim 19 , wherein the bias generator circuit comprises a pair of resistors connected to the power supply and the sensing resistor, one of said pair of resistors having a resistance that is three time greater than a resistance of the other of said pair of resistors.

24. The control system of claim 23 , wherein a voltage value at a junction between the resistors of said pair of resistors is one quarter a voltage value of the power supply.

25. The control system of claim 19 , wherein the magnitude of the voltage across the sensing resistor is the same regardless of an ON/OFF state of the heating control circuit.

Assignees

• Resmed Ltd

Inventors

• Vos Adrian Ashley
• Huby Ronald James
• Tang Zhuo Ran

Classifications

• G01K13/02

  for measuring temperature of moving fluids or granular materials capable of flow · CPC title

• A61M16/1095 Primary

  in the connecting tubes · CPC title

• A61M16/0003 Primary

  Accessories therefor, e.g. sensors, vibrators, negative pressure · CPC title

• A61M16/16

  Devices to humidify the respiration air {(A61M16/1045 takes precedence)} · CPC title

• A61M16/0057

  Pumps therefor · CPC title